The Calls of the Red Squirrel: a Contextual Analysis of Function

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I examined the context of occurrence of five calls used by adult red squirrels (Tamiasciurus hudsonicus) in the field, in an attempt to 1) determine whether rattles and screeches function as threat displays in the context of territorial defence; and 2) identify the possible function of those calls not involved in territorial defence. Focal squirrels were much more likely to approach aggressively, attack, or chase their opponents, and the latter much more likely to retreat, after the focal squirrels had screeched than when they did not screech. I interpret the screech as a threat call that honestly signals a territory owner's intention to chase out an intruder. The rattle, which SMITH (1978) considered to function in territorial defence, was not associated with aggression from the caller when used independently of the screech. It was significantly associated with courting approaches by males towards females during the mating season. In addition, the rattle occurred in association with screeches more often than expected, and the screech almost never occurred without rattles, suggesting that the functions of the two calls are linked. I discuss the evidence that the rattle is a self-advertisement signal, or "signature". On the other hand, squirrels were less likely to be aggressive when they rattled and screeched if they also barked than if they did not; and recipients were concomitantly less likely to retreat, but not more likely to show aggression. I suggest that callers emitted barks after rattles and screeches in response to the other squirrel's not leaving after being threatened, rather than to signal a lower probability of aggression. Barks not accompanied by rattles or screeches had no predictable effect on either the caller's or the recipient's subsequent behaviour. I tentatively interpret the call as a signal emitted in motivational conflict situations, to elicit a change in the recipient's behaviour that would help the caller decide what to do next (HINDE, 1981). The growl was a defensive threat call that accompanied close-range aggression by the caller, but that was not followed by the immediate retreat of the opponent. Finally, the buzz was associated with non-aggressive approaches by the caller. I discuss the function of the screech in the light of the theory of animal conflicts, and suggest that it may convey information contingent upon the recipient's response (WILEY, 1983), rather than unconditional information.